The driver of a New York commuter train that derailed on Sunday, killing four people, told federal investigators he "zoned out" shortly before the crash, the driver's labour union leader said.
The seven-car train was traveling at 82 miles per hour (132 km per hour), nearly three times the speed limit for the curved section of track where it crashed, investigators have said. The driver, William Rockefeller, 46, applied the brakes five seconds before it derailed.
The crash also critically injured 11 people and snarled travel for the roughly 26,000 regular commuters on the Metro-North Hudson line that serves suburbs north of New York City.
On Tuesday, Rockefeller told National Transportation Safety Board investigators that "he nodded. He zoned out," Anthony Bottalico, the general chairman of the driver's labour union, the Association of Commuter Rail Employees, told Reuters.
Rockefeller told investigators that "by the time he realised (what was happening) it was almost into the curve," Bottalico said. "He put the train into neutral and put the brakes on immediately. That's what he acknowledged he did."
The NTSB has cautioned that its investigation would continue for weeks, if not months, and it was far from reaching a conclusion on the cause.
Alcohol tests on Rockefeller came back negative, NTSB member Earl Weener told a news conference on Tuesday, adding the results of drug tests were still pending.
The train might have benefited from a Positive Train Control (PTC) system to stop or slow a speeding train, Weener said.
"For more than 20 years, the NTSB has recommended implementation" of PTC, Weener said. "Since this is a derailment, it's possible that PTC could have prevented it."
Railroad experts have been advocating for PTC systems for years, but they are expensive and complicated and often incompatible for all trains within a single transit system.
The Metropolitan Transportation Authority, which runs Metro-North, said it began work to install Positive Train Control in 2009 with a goal of implementing it by 2015. The authority said it has budgeted nearly $600 million, with at least another $300 million needed, and even then was unlikely to meet the 2015 deadline.